Beede.J Carboniferous Invertebrates. 67 



ton, Topeka, Beaumont, Grand Summit. Widely distributed, 

 but moderately rare throughout the Coal Measures and base of 

 the Permian. Abundant near the base of the Permian. 



The individual variation of this species is very great. In 

 most of the larger specimens the width is considerable greater 

 than the length as indicated by the above measurements. The 

 distinctness of the plications varies with age, being very faint 

 in young specimens and very distinct and sharp in old ones. 

 Young specimens are much less convex and comparatively 

 longer than the old ones. The comparative height of the car- 

 dinal area varies greatly, some- specimens having the beak only 

 moderately elevated. 



CHONETES. 



Fisher and Waldheim. Oryct. du Gouv. de Moscou, pt. II, p. 134, pi. XXVI, ft". 8, 9, ( 1837 ). 



Hall and Clarke, Pal. N. Y., VIII, pt. I, Brachiopoda, p. 303, pi. XV-", ff. 11-13, pi. XVI, if. 1 11. 



14, 15, 18-27, 32-36, 39, 43, 44, 48, ( 1892 ). 



Prior to 1844 species belonging to this genus were described 

 under the generic terms Pecten, Hysterolythes, Terebratulites , 

 Leptsena, Orthis, Spirifera, Strophomena, Productus, and Delthyris. 



Since that time the genus has been better understood. 



After giving the generic description (loc. cit.) , Hall and Clarke 

 say of the genus : "Choneles is remarkable for the persistence 

 of its characters. From its appearance in the middle of the 

 Silurian to its disappearance in the Permian, this type of struc- 

 ture has been maintained with few essential modifications. On 

 account of this stability in its features it is difficult to establish 

 any satisfactory subdivision of its members, especially since the 

 genus has been left more compact by the recent elimination of 

 some of its more aberrant forms." 



The following is a summary of the sections of the genus, as 

 compiled by them, now accepted by leading authorities; these 

 sections are mechanical and arbitrary : 



I. — Concentricce, those with concentric folds or undulations, like C. con- 

 a ntrica. 



II. — Striata , those with more than thirty radiating striae. 

 111.— Flicosa , those with less than thirty striae. 

 IV. — Rugosa , those with rugose radiating striae. 



V. — GhrandicostatcBi those with high, strong radiating costae. 

 \\. -Lnres, those with smooth shells. 



